To succeed in school, children must master the “three R’s”—reading, writing and arithmetic—but not all students readily grasp these basic skills. Among English-speaking children, an estimated 2 to 15 percent have trouble reading or spelling, problems broadly classified as dyslexia. From 1 to 7 percent struggle to do math, a disability known as dyscalculia. Statistics vary; dyslexia appears to be more common, for example, among English speakers than among speakers of highly phonetic languages, such as German or Italian. Nevertheless, it is fair to say that at least one child in most elementary school classes in the U.S. suffers from dyslexia or dyscalculia.

These learning disabilities defy easy explanation. Neither is the result of faulty eyesight or hearing, both of which can also delay language acquisition but are easily corrected using glasses or hearing aids. Instead children with dyslexia and dyscalculia have working sensory organs, apparently normal sensory and motor development and, sometimes, above-average intelligence.